What Does “A Swarm of Krill” Mean?
“Swarm” is the collective noun for a group of krill, and unlike many of the terms on this site, it’s not a borrowed or whimsical word, it’s a direct, accurate description of real krill behavior. These small, shrimp-like crustaceans gather in immense numbers, forming some of the densest and largest animal aggregations found anywhere in the ocean.
Krill swarms can stretch for kilometers, reach densities of tens of thousands of individuals per cubic meter, and in extreme cases have been estimated to weigh millions of tons. Swarming also isn’t just passive clustering: krill perform coordinated vertical migrations, rising toward the surface at night to feed on phytoplankton and sinking back into deeper water by day, moving together the entire time.
Example: “A swarm of krill lit up the dark water with a faint blue glow.”
Related: Collective Nouns for Crustaceans · What Is a Group of Krill Called?